I heard today that deuterium for nuclear fusion could be extracted from the Oceans, in which it is present in "heavy water." I heard this claim:
"Deuterium is distributed uniformly with Ocean depth."
This contradicted my naive expectation that deuterium density would increase with depth, on account of it being in "heavy water." For example, salinity increases with depth. I asked, and received two contradictory explanations.
The first was that because powerful waves and Ocean currents mix Ocean water, gravity is negligible. This surprised me; I thought that Ocean's were stratified, with predominantly tangential, rather than vertical, currents.
The second explanation was that my view of seawater is naive - that I should think of seawater not as heavy and regular water molecules, but as a soup of weakly interacting deuterium, the normal hydrogen isotope and oxygen, forming and breaking water and heavy water molecules with a short time-scale. If so, apparently, deuterium density and the normal hydrogen isotope would be distributed evenly with depth. This did not help me, because, I then naturally wondered why deuterium's density doesn't increase with depth, since it is heavier than hydrogen-1?
Is the claim correct? and if so, what is really going on? I have the feeling that Ocean behaviour with depth might be non-trivial...